Holding an object requires smooth interaction between high and low brain frequencies

Researchers have identified a neuronal mechanism enabling people to maintain constant contraction force.

Holding a glass requires a high degree of precision in the force we apply with the hands. Although effortless, this task requires continuous adjustment of the force and finger position based on sensory information. The research team set out to better understand the neuronal mechanisms enabling us to achieve this demanding skilled task.

The researchers recorded magnetoencephalographic (MEG) brain activity from adult volunteers who pinched the handle of a device to record grip force. The analysis focused on the coupling of the brain activity with minor hand vibrations during the steady pinch.

The results showed that the brain regulates the grip force based on the low-frequency, below 3 Hz, content of sensory signals generated by proprioceptors in the hand. The proprioceptors are sensory organs that monitor the position of body parts.

Researchers recorded MEG signals from healthy volunteers (left) who pinched the handle of a device that monitored the contraction force (right). The results showed that the brain speaks to the muscles at 20 Hz (rightwards arrow) and listens to them at 3 Hz (leftwards arrow). Picture: Modified from Bourguignon et al. 2017.

The finding contradicts previous studies, which had contemplated the possibility that the brain would make use of signals at higher frequencies around 20 Hz. Indeed, 20 Hz is the dominant frequency of the oscillatory brain activity that arises from the sensorimotor cortex, the part of the brain that controls motor actions and monitors tactile and proprioceptive information. Moreover, the signals from the brain and the contracting muscle are coherent at 20 Hz.

“The research team now demonstrated that the brain speaks to the muscles and listens to them at different frequencies, at 20 Hz and at less than 3 Hz, respectively”, describes researcher Mathieu Bourguignon.

This study was carried out at the Department of Neuroscience and Biomedical Engineering of the Aalto University and was published in the Journal of Neuroscience. The lead author, Mathieu Bourguignon is currently working at the ULB Neuroscience Institute in Brussels.